uwb-rescue-locator
Lucas-Poulos
Components (29)
| Reference | Value | Description |
|---|---|---|
| Q1 | AO3401A | |
| Q2 | FS8205A | |
| U1 | DW01A | |
| U2 | MCP73831T-2ACI/OT | |
| U4 | DWM3001C | |
| U5 | TPS7A0233PDBVR | |
| BT1 | 3.7V LiPo (1S, JST-PH 2-pin) | |
| C1 | 0.1uF | |
| C2,C3,C7 | 4.7uF | |
| C4 | 10uF | |
| C5,C6,C16 | 100nF | ADC sampling capacitor across R12, stabilising the 1M/1M divider tap for the nRF52833 SAADC. The divider's ~500k source impedance is high for the SAADC, so this reservoir plus a long acquisition time setting in firmware is what makes the reading accurate. |
| C11 | 1uF | |
| C12 | 2.2uF | |
| D1,D3 | ESD5B5.0ST1G | USB VBUS ESD/TVS protection at the J1 charging port -- the gap flagged by the analyzer (UC-002) and already listed as 'not yet placed' in libs/components.csv. Same part as the battery-line TVS D1: 5V reverse standoff, 5.8V clamp, SOD-523, which suits a 5V USB VBUS rail. Cathode to VBUS, anode to GND, placed as close to J1 as layout allows. |
| D2 | Green,LED | Charge status LED -- driven from MCP73831 STAT (U2 pin 1, power_bms.kicad_sch),Charge-status LED driven by MCP73831 (U2) STAT pin through R10. The MCP73831 typical application circuit shows this LED; this board previously documented it but never placed it, leaving STAT floating with no way to tell charging from charged. Anode to +VBUS-side rail through R10, cathode to STAT (the MCP73831 sinks when charging). |
| D3 | LED | System status LED -- intended to be driven from a DWM3001C (nRF52833) GPIO (not yet allocated) |
| J1 | USB4125-GF-A | |
| J3 | Conn_ARM_JTAG_SWD_10 | |
| R1 | 100k | |
| R2 | 100 | |
| R3,R10,R11 | 1k | Series resistor for D2 charge-status LED. ~3mA from the ~5V VBUS rail; confirm rail and value at wiring time.,Series resistor for D3 system-status LED.,Series resistor for the D2 charge-status LED. ~1.3mA at 3.3V with the LTST-C191KGKT's ~2.0V Vf ((3.3-2.0)/1k) -- deliberately dim. This is a wearable on a small cell, and the MCP73831 STAT pin can sink up to 25mA, so the constraint here is battery life, not the driver. |
| R4 | 6.8k | |
| R5,R6 | 5.1k | |
| R11,R12 | 1M | Battery-voltage monitor divider (R11 high side to VBAT, R12 low side to GND, tap to a NINA-B400 analog-capable GPIO). 1M/1M halves VBAT's 4.2V full-charge to 2.1V, safely inside the nRF52833 SAADC range at a 3.3V reference. TRADEOFF WORTH KNOWING: 4.2V/2M = ~2.1uA continuous, which is comparable to the module's own ~2.6uA System ON sleep current (UBX-19049405 R09 Table 12) -- i.e. this divider roughly doubles standby drain. If runtime matters more than always-on battery reporting, gate the divider's low side with a small FET driven by a GPIO and sample on demand. |
| SW1 | SOS | User/SOS momentary tactile button, 4.5x4.5mm SMD, 2.2N actuation force, 100k cycles. Intended to drive a NINA-B400 GPIO low when pressed, with the nRF52833's internal pull-up enabled in firmware (no external pull-up part needed). Debounce in firmware. NOTE: actuation force and travel should be re-checked for glove/cold-weather use -- this is a rescue device. |
| TP1 | +3V3 | Regulated 3.3V rail out of the MCP1700 LDO (regulation.kicad_sch). |
| TP2 | VBAT | Protected battery rail out of the DW01A/FS8205 pair (power_bms.kicad_sch). Lets the cell and protection chain be checked independently of the regulator. |
| TP3,TP4 | GND | Ground for scope probing.,Second ground, so a meter and a scope can both attach. |
| TP5 | FW_MARKER | Spare nRF52833 GPIO for firmware to toggle around a ranging exchange, making tag-side timing visible on a scope. GPIO not yet allocated. |